196
CARDIOVASCULAR PHYSIOLOGY CONCEPTS
3.
The correct answer is “a” because when
cardiac output is reduced, oxygen deliv-
ery to organs is reduced (choice “c” is
therefore incorrect) because of reduced
organ flow. If this flow reduction occurs
under conditions of normal organ oxygen
consumption, there will be an increase in
oxygen extraction (choice “d” is there-
fore incorrect), which will reduce Sv02.
Choice “b” is incorrect because decreased
oxygen consumption would increase
SvOr Note that the reduced Sv02 is not a
consequence of reduced Sa02 in this case
because that value is within the normal
range.
4.
The correct answer is “a” because capil-
lary plasma oncotic pressure opposes fil-
tration; therefore, decreasing this pressure
enhances filtration. Choices “b” and “c”
are incorrect because decreasing venous
pressure or increasing precapillary resis-
tance reduces capillary hydrostatic pres-
sure, thereby decreasing filtration. Choice
“d” is incorrect because increased tissue
hydrostatic pressure opposes filtration.
5.
The correct answer is “b” because the
net driving force, calculated from the
given values, is -2 mm Hg, which causes
reabsorption. Choices “a” and “c” are
incorrect because the net driving force is
a negative value.
6.
The correct answer is “d” because
protein deficiency leads to hypopro-
teinemia, which reduces plasma oncotic
pressure, thereby increasing net capil-
lary fluid filtration. Choice “a” is incor-
rect because decreased blood volume
caused by dehydration in this child
would decrease capillary hydrostatic
pressure and fluid filtration. Choice “b”
is incorrect because decreased inter-
stitial oncotic pressure opposes filtra-
tion. Choice “c” is incorrect because
increased capillary fluid reabsorption
would decrease edema and ascites.
7.
The correct answer is “c” because
increased postcapillary/precapillary
resistance ratio caused by arterial (pre-
capillary) vasodilation increases capil-
lary hydrostatic pressure and fluid filtra-
tion. Choice “a” is incorrect because a
decreased capillary hydrostatic pressure
decreases fluid filtration. Choice “b” is
incorrect because a decreased capillary
filtration constant decreases net filtra-
tion. Choice “d” is incorrect because a
reduced venous pressure decreases capil-
lary pressure and filtration.
ANSWERS TO PROBLEMS AND CASES
PROBLEM 8-1
During the period of ischemia, the P02 and
oxygen content of the static blood within
the microcirculation fall as oxygen diffuses
from the blood into the tissues. When blood
flow is restored, this oxygen-depleted blood
is washed out of the tissue; a sample of this
blood will have reduced P02 and oxygen
content. During the phase of reactive hyper-
emia, the increased blood flow and oxygen
delivery to the tissue is greater than what is
needed to supply the oxidative metabolism
of the tissue. If the ratio of oxygen delivery
to oxygen consumption is increased above
normal, then the venous oxygen content and
P02 will increase. As the balance is restored
toward the end of the hyperemic response,
the P02 will normalize.
PROBLEM 8-2
a) The net driving force, NDF = [(Pc —
P.) -
o(jic
- 71.)]. Substituting the given values,
the NDF = 7 mm Hg.
NDF = [22 - (-3)] - 0.9 [(26 - 6)]
= 7 mm Hg
b) Because the NDF is greater than zero, filtra-
tion is occurring.
c) The net rate of fluid movement, J = Kp • A
(NDF). Therefore, if the product of Kp and
A is doubled, then J (the filtration in this
problem) is doubled because the NDF ^ 0.
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